Since we are in a community property state, and the surviving one of us would get everything anyway, is there any need to have a trust?

In that specific case, probably not. But what if you both die in a plane crash or some other event? What happens then?

My understanding is that California has particularly orneorous probate court fees, so even people with realatively modest assets are well advised to arrange their affairs so as to avoid them. You can probably do that by making sure everything is properly titled and accounts have the proper beneficiaries, but make sure you understand California law on the point.